Orthogonal Frequency Division Multiple Access (OFDMA) modulation schemes have been proposed for downlink transmissions over an air interface in next generation communication systems, for example, a 3GPP (Third Generation Partnership Project) E-UTRA (Evolved UMTS Terrestrial Radio Access) communication system, a 3GPP2 Phase 2 communication system, and various IEEE (Institute of Electrical and Electronics Engineers) 802.16 communication systems. In an 802.16m OFDMA communication system, a frequency channel, or bandwidth, is split into multiple contiguous Physical Resource Units (PRUs). Each PRU comprises 18 consecutive frequency sub-carriers, which sub-carriers are orthogonal to each other, by six (6) or seven (7) Orthogonal Frequency Division Multiplexing (OFDM) symbols. A grouping of multiple PRUs is known as a sub-band, or cluster, which typically consists of four (4) PRUs. Under the 802.16m standards, a base station (BS) may assign the PRUs to mobile stations (MSs) on a sub-frame basis.
In the 802.16m standards, a logical resource unit (LRU) is the basic logical unit for distributed and localized radio resource allocation. One mapping scheme, known as a logical localized resource unit (LLRU), maps a LRU into multiple contiguous sub-carriers (a contiguous, or localized, PRU). The size of the LLRU equals the size of a PRU, that is, 18 sub-carriers by six or seven OFDM symbols. Localized mapping is used for Frequency Selective Scheduling (FSS), wherein transmission errors are minimized by scheduling a mobile station (MS) for one or more contiguous sub-carriers where the UE is known to have a good downlink channel, based on narrowband channel feedback from the MS. A second mapping scheme, known as a logical distributed resource unit (LDRU), maps a LRU into multiple sub-carriers that are distributed throughout the frequency bandwidth (a non-contiguous, or distributed, PRU). The size of the LDRU also is equal to the size of a PRU, that is, 18 sub-carriers by six or seven OFDM symbols. Distributed mapping is used for Frequency Diverse Scheduling (FDS) and utilizes frequency diversity to achieve a desired throughput level, and thus an LRU may be distributed among multiple sub-carriers without channel feedback or only wideband channel feedback.
Further, the 802.16m standards provide for division of each downlink (DL) and uplink (UL) sub-frame into a number of frequency partitions. Each frequency partition consists of a set of PRUs across the total number of OFDM symbols available in the sub-frame. Each frequency partition then may be allocated to a different coverage area, such as a cell or a sector of a cell. The distribution of frequency partitions among multiple coverage areas is known as fractional frequency reuse (FFR). However, the 802.16m standards fail to specify a specific physical layer structure, that is, a scheme for allocating frequency partitions to the different coverage areas or for mapping the LLRUs and LDRUs to the different frequency partitions/coverage areas.
Therefore, a need exists for method and apparatus for allocating frequency partitions to different coverage areas and maps LLRUs and LDRUs to the different coverage areas.
One of ordinary skill in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of various embodiments of the present invention. Also, common and well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.